Barrier operator having system for detecting attempted forced entry

ABSTRACT

A movable barrier or garage door operator has a barrier drive for moving the movable barrier or garage door between open and closed positions. Motion of the barrier is detected by a tachometer connected to the barrier drive or by upper and lower barrier travel limit switches. A test is made to determine if the barrier has been commanded to be in a closed state and to determine if a preselected time interval has elapsed following closure of the barrier. When both of those conditions are present and the door is moved upward without authorization an alarm signal is generated and can signal the barrier drive to apply a closing force. The timer prevents the barrier from being closed on a person or obstacle during normal operation and prevents injury. An obstacle detector also prevents unwanted closure on an obstacle.

This application is a continuation of application Ser. No. 08/443,178 filed May 17, 1995, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates, in general, to barrier operators and, in particular to a garage door operator including a system for detecting when an attempt is made to force open a closed garage door.

Several garage door operator systems are available on the market for maintaining a garage door either in a closed or open position. It is clear that the systems should be relatively easy to use and should be able to open the door relatively rapidly to allow quick and easy access to the garage. In addition, many systems are provided which include detectors, pressure detectors and the like that sense when the garage door is being brought down and the bottom edge of the door comes in contact with an obstacle prior to the door reaching the fully closed position. These systems are important because they prevent the garage door from closing on people, pets or small objects and, therefore, prevent personal injury and property damage. One of the drawbacks of such systems, however, is that for some such systems, when the door has been closed, if a lifting force is applied to the door, or instance by an unwanted intruder grabbing the handle of the door and attempting to raise it by jacking the door or the like, some systems through a force measurement routine, automatically cause the door to be opened, in order to prevent what the garage door operator senses might be potential harm. Of course, if the person operating the door is attempting to break and enter the garage for nefarious purposes and it is important that while the system prevents harm, the system also be provided such that the door cannot be forced open if the operator does not want it to be and if no persons or property are in danger.

A system available from the Stanley Company provides a garage door operator having upper travel limit and lower travel limit switches associated therewith. The switches may be set or moved so that the limits of travel may be changed. In the Stanley system, for instance, if the door has reached a nominal closed position and the operator has its down limit switch position changed, the door will actually dynamically track changes in the switch position and open or close according to switch commands.

Mechanical systems may be available that in effect, jam the door closed; however, once these systems are placed in effect, if a person not knowing that the door is down and effectively mechanically locked attempts to open the door the garage door operator then attempts to lift the door against the locking mechanism and the garage door operator may be inadvertently damaged thereby or, at the very least, not open the door because it is locked.

What is needed then is a system which provides a sensing modality for a garage door or other barrier operator which, while maintaining all safety features to prevent personal injury or property damage due to unwanted closing of the door, nevertheless senses when an intruder attempts to open the door and prevents the door from being opened by a positive drive force provided by the garage door operator motor.

SUMMARY OF THE INVENTION

The invention relates, in general, to a barrier system operator and, in particular, to a garage door operator which while having all safety features for preventing personal injury and property damage due to inadvertent closing of the garage door, nevertheless provides a positively actuated door closure system which prevents forcing the door once it has closed without having detected any objects underneath it. The system includes a barrier drive including an electric motor which may be connected to a belt, chain or screw drive. Means are provided for detecting motion of the movable barrier. These means may include a motor tachometer, upper and lower limit switches and the like. Means are also provided for detecting when a barrier command signal has been given to the barrier drive so that when a door has been commanded by a radio frequency control, the keypad control, indoor wired control or the like to open, the door may be automatically opened. The system also includes a storage device for storing the commanded state of the barrier drive which may be a microcontroller or a microprocessor in combination with a memory or some other integrated circuit device capable of storing digital or analog information. The commanded state is stored and is then compared in a comparator means with the position indicated by the barrier detection. In the event that the comparison of the barrier state signal and the barrier position signal indicates that the system already has been in a lowered position, usually for given time intervals, such as 27 seconds and attempt is made to raise the door causing unwanted motion of the door when there has been no up command given, an alarm signal is generated which may be passed through electronic and electromechanical logic to the door motor causing the door motor to provide thrust to the door to hold the door in the closed position.

In the alternative, the system may also provide a signal to operate a visual or audio alarm or to call over a telephonic or other wired system to a police department or to a security service to indicate that the system is being broken into.

It is a principal object of the present invention to provide a barrier operator for opening and closing a movable barrier which includes an electronic system for detecting when forced entry is being attempted on the carrier and for preventing the barrier from being opened.

Other objects of this invention will become obvious to one of ordinary skill in the art upon a perusal of the following specification and claims in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus comprising a garage door operator and embodying the present invention;

FIG. 2 is a block diagram of a portion of the head unit and associated controls of the apparatus shown in FIG. 1;

FIG. 3 is FIGS. 3A-3C are a schematic diagram showing details of the circuit shown in FIG. 2;

FIG. 4 is a flow chart of a top level flow diagram for the apparatus embodying the present invention;

FIG. 5 is a flow diagram of an upper limit routine;

FIGS. 6A and 6B are a flow diagram controlling travel upward;

FIG. 7 is a flow diagram of a down limit routine;

FIGS. 8A and 8B are a flow chart of a downward or closing movement routine;

FIG. 9 is a flow chart of a barrier closed routine; and

FIG. 10 is a flow chart of an auto-reverse time delay routine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and especially to FIG. 1, more specifically a movable barrier door operator or garage door operator is generally shown therein and includes a head unit 12 mounted within a garage 14. More specifically, the head unit 12 is mounted to the ceiling of the garage 14 and includes a rail 18 extending therefrom with a releasable trolley 20 attached having an arm 22 extending to a multiple paneled garage door 24 positioned for movement along a pair of door rails 26 and 28. The system includes a hand-held transmitter unit 30 adapted to send signals to an antenna 32 positioned on the head unit 12 and coupled to a receiver as will appear hereinafter. An external control pad 34 is positioned on the outside of the garage having a plurality of buttons thereon and disposed to communicate via radio frequency transmission with the antenna 32 of the head unit 12. An optical emitter 42 is connected via a power and signal line 44 to the head unit. An optical detector 46 is connected via a wire 48 to the head unit 12.

The head unit 12 has a wired wall control panel 43 connected to it via a line or wire 43 a, as is shown in FIG. 2. More specifically, the wall control panel 43 is connected to a charging circuit 70 and a discharging circuit 72 coupled via respective lines 74 and 76 to a wall control decoder 78. The wall control decoder 78 decodes closures of a plurality of switches 80, 82 and 84 in the wall circuit. The wall control panel also includes a light emitting diode 86 connected by a resistor 88 to the line 43 a and to ground. Switch 80 is the command switch, switch 82 is the work light switch and switch 84 is the vacation switch. Switch closures are decoded by the wall decoder 78 which sends signals along lines 90 and 92 to a motor control 94 coupled via motor control lines 96 to an electric motor 98 positioned within the head unit. A tachometer 100 receives a mechanical feed from the motor 98 and provides feedback signals on lines 102 to the motor controller.

The receiver unit also includes an antenna 110 coupled to receive radio frequency signals either from the fixed RF keypad 34 or the hand-held transmitter 30. The RF signals are fed to a radio frequency receiver 112 where they are buffer amplified and supplied to a bandpass circuit 114 which outputs low frequency signals in the range of 1 Hz to 1 kHz. The low frequency signals are fed to an analog-to-digital converter 116 that sends digitized code signals to a radio controller 118. The radio controller 118 is also connected to receive signals from a non-volatile memory 120 over a non-volatile memory bus 122 and to communicate via lines 124 and 126 with the motor controller 94. A timer 128 is also provided, coupled via lines 130 with the radio controller, a line 132 with the motor controller and a line 134 with the wall control decoder 78. A barrier travel limit detection device 190 includes an up limit detector 190 a and a down limit detector 190 b that sends signals to pins P20 and P21 of the microcontroller 282(as depicted in FIG. 3b). The obstacle detector comprising the emitter 42 and detector 46 send signals to pins P03 and P30 of the microcontroller 282(as depicted in FIG. 3b) indicating when an obstacle is blocking the path of the door.

Referring now to FIG. 3, the system shown in FIG. 3 is shown therein with the antenna 110 coupled to a reactive divider network 250, comprised of a pair of series connected inductances 252 and 254 and capacitors 256 and 258, which supplies an RF signal to the buffer amplifier 112 having an NPN transistor 260 connected to receive the RF signal at its emitter 261. The NPN transistor 260 has a capacitor 262 connected to it for power supply isolation. The buffer amplifier 112 provides a buffered radio frequency output signal on a lead 268. The buffered RF signal is fed to an input 270 which forms part of a super-regenerative receiver 272 having an output at a line 274 coupled to the bandpass filter 114 which provides output to a comparator 278. The bandpass filter 114 and analog-to-digital converter provide a digital level output signal at a lead 280 which is supplied to an input pin P32 of an 8-bit Zilog microcontroller 282.

The microcontroller 282 may have its mode of operation controlled by a programming or learning switch 300 positioned on the outside of the head unit 12 and coupled via a line 302 to the P26 pin of the microcontroller 282. The wired control panel 43 is connected via the lead 43 a to input pins P06 and P07 The microcontroller 282 has a 4 MHz crystal 328 connected to it to provide clock signals. A force sensor 330 includes a bridge circuit having a potentiometer 332 for setting the up force and a potentiometer 334 for setting the down force, respectively connected to inverting terminals of a first comparator 336 and a second comparator 338. The comparator 336 sends an up force signal over a line 339 a. The comparator 338 sends a down force signal over the line 339 b, respectively to pins P04 and P05 of the 8-bit microcontroller 282. Although details of the operation of the microcontroller in conjunction with other portions of the circuit will be discussed hereinafter, it should be appreciated that the P01 pin of the microcontroller is connected via a resistor 350 to a line 352 which is coupled to an NPN transistor 354 that controls a light relay 356 which may supply current via a lead 358 to a fight in the head unit or the like. Similarly, the pin P000 feeds an output signal on a line 360 to a resistor 362 which biases a base of an NPN transistor 364 to cause the transistor 364 to conduct, drawing current through the coil of the relay an up relay 366 causing an up motor command to be sent over a line 90 to the motor 98. Finally, the P02 pin sends a signal through a line 370 to a resistor 372 via a line 374 to the base of an NPN transistor 376 connected to control current through a coil of a down control relay 378 which is coupled by one of the leads to the motor 98 to control motion of the motor 98.

Electric power is received on a hot AC line 390 and a neutral line AC line 392 which are coupled to a transformer 393 at its primary winding 394. The AC is stepped down at a secondary winding 395 and is full wave rectified by a full wave rectifier 3%. It may be appreciated that, in the alternative, a half wave rectifier may also be used.

A plurality of filter capacitors 398 receive the full wave rectified fluctuating voltage and remove some transients from the voltage supplying a voltage with reduced fluctuation to an input of a voltage regulator 400. The voltage regulator 400 produces a 5-volt output signal available at a lead 402 for use in other portions of the circuit.

Referring now to FIG. 4, a top level routine is shown therein which is entered every two milliseconds upon at timing interrupt in a step 500. The routine then enters a variety of other routines depending upon the value of a state number. When the state number is 2 an upper limit routine is entered in a step 502. If the state number is 1, a traveling up routine is entered in a state 504. If the state is 5, a down limit routine is entered in a step 506. If the state is 4, a traveling down routine is entered in a step 508. If the state is 6, a barrier halt or stopped in middle routine is entered in a step 510. If the state is 0, an auto-reverse time delay routine is entered in a step 512. When any of the aforementioned routines 502 through 512 are exited, a return step 514 is entered and other portions of code not pertinent to this invention are executed.

In the event that the state equals 2, the routine 502 is entered as may best be seen in FIG. 5 wherein the upper limit switch has indicated that the door has reached the upper end of its authorized travel, the motor is switched off and a watchdog timer is started in a step 514. The work light command flag is set in step 516 to toggle the work light on. In a step 518, a radio command or wall control command flag is tested for and, if set, the state is set to 4. In a step 520, the routine is exited and return is switched to the step 514. In the event that the state has been set equal to 4, in step 518 at the next 2 millisecond interval, control is transferred to the routine 508.

In the event that the state has been set equal to 1, control is transferred to a barrier traveling up or a barrier opening routine shown in FIGS. 6A and 6B. In a step 522, the work light is turned on and in the event that the light was off, a delay of 40 milliseconds is then provided to turn on the up motor output, the down motor output is turned off and the hold door closed flag is cleared. In a step 524, after a start up delay of 1 second the rpm period of the tachometer is tested against the look up force and if the rpm period is too brief, a state is set to indicate that the door has stopped in mid travel. In a step 526, a test is made to determine whether the one second timer has exceeded one second and whether the rpm period is below the set force limit indicating that the door has been halted in an unwanted manner. If it is not, control is transferred to a step 528 wherein the state variable is set to 6, following which the routine is exited in a step 530. In the event that the decision in step 526 is positive, the up limit input is tested. If the voltage is low, it is increased. If it is high, the debounce is decreased. Control is then transferred to a test step 532 to test whether the limit debounce is greater than 24 milliseconds. If it is, the state is set equal to 2 in a step 534 and the routine is exited in a step 536. If the limit debounce is less than 24 milliseconds, control is transferred to a step 540 where a 27 second time out is decremented and tested for. If the time out is zero, the state is set as indicating that the door has stopped in mid travel. A step 542 is executed to test for either a radio or wall control command flag having been set and, if so, the state is set as stop in mid travel. The routine is then executed in a step 544.

In the event that the state has been set equal to 5, a routine 506 to handle down limits, as shown in FIG. 7, is entered. In a step 550, a hold door closed flag is tested to determine whether it is set or not. If it is not set, control is transferred to a step 552 to determine whether the 27 seconds timer has timed out following the down limit having been set, indicating that the door has safely closed and did not contact an obstruction or obstacle. In the event that the hold door closed flag has been set, as tested for in step 550, control is transferred to a step 554 testing whether the down limit indicates the door is open and whether the motor has been given enough current or turned on long enough to provide 10 rpm pulses. In the event that the 27 second clock has not been timed out as indicated by step 552, control is transferred to a step 556, switching the motor off, and starting a watchdog timer. Control is then transferred to a step 558 to determine if the work light command flag has been set and, if it has, the work light is toggled. Control is then transferred to a step 560, testing for whether there is a radio command or wall control command flag. If so, the state is set equal to 1 and the routine is exited in a return step 562. In the event that the down limit does not indicate that the door is open and the motor has been turned enough to give 10 rpm pulses, control is transferred to a step 564 setting the state equal to 4 and setting the hold door closed flag. The state equal 4 indicates that the door is to be traveling down, thereby causing the barrier to close after the 27 second limit has timed out.

In the event the state has been set equal to 4 to command the door to travel down, the routine 508 is entered as shown in FIGS. 8A and 8B. In a step 570, the work light is turned on, and if the light had previously been off, a delay of 40 milliseconds occurs following which down motor output is turned on and the up motor output is turned off, the watchdog is also started. In a step 572, a test is made to determine whether the 1 second timer has exceeded 1 second and whether the rpm period is indicative of a force limit having been exceeded. If so, indicating that the door is stalled on an obstacle, control is transferred to a step 574, setting a state equal to zero and the routine is exited in a step 576. If the door has not been indicated to be stalled by the step 572, control is transferred to a step 578 testing the status of the down limit input. If it is low, the debounce is increased. If it is high, the debounce is decreased. In a step 580, the limit debounce is tested to determine whether it is greater than or equal to 24 milliseconds. If it is, the state is set equal to 5 in a step 582 and the routine is exited in a step 584. If it is not, the 27 second time out is decremented and tested to determine if it is zero. If it is zero, the state is set equal to zero in a step 586. In a step 588, a test is made to determine whether the radio or wall control command flag has been set and, if so, the state is then set equal to 6. In a step 590, as shown in FIG. 8B, the timer associated with the optical detector is tested to determine whether it is greater than 10 milliseconds and, if it is, indicating that an obstacle is blocking the light path, the state is set equal to zero to cause the auto-reverse routine 512 to be entered following exiting from this routine. It will be entered on the next interrupt which is in less than 2 milliseconds. Control is then transferred to a step 592, testing whether the motor speed indicated that the door had been forced upward. If it is not the routine is exited in a step 594. If the rpm sensing indicates that the door has been forced upward, a test is made in the step 596 to determine if the command is still valid, indicating the door is to move upward. If it is not, control is transferred to a step 598 setting the state equal to zero which will cause the door to auto reverse and move down. Control is then transferred to a step 600 exiting the routine.

In the event that the state has been set equal to 6, the routine 510 shown in FIG. 9 is entered. A test is made to determine whether the motor motion indicates that the door has been forced upward. If so, a flag is set to turn off the light and the electric motor is switched off and the watchdog is started. If the worklight command flag has been set in a step 604, the work light is then toggled. In a step 606, a test is made to determine whether the radio command or wall control command flag has been set and, if it has, the state is then set equal to 4 which will cause entry of the traveling down routine 508. The routine is then exited in a step 608.

In the event that the state has been set equal to zero indicating that an auto reverse is to be commanded, the routine 512 is entered in a step 620, the motor is turned off and a watchdog timer is started. In the step 622, the delay timer is decreased and if 0.5 seconds has expired, the state is set equal to 1 to cause the door to travel upward on the next 2 millisecond interrupt. In a step 624, a test is made for the radio command or wall control command flag being set. If it has, the stopped in middle routine 510 will be entered on the next interrupt. The routine 512 is then exited in a step 626.

While there has been illustrated and described a particular embodiment of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention. 

What is claimed is:
 1. A barrier operator for opening and closing a movable barrier, comprising: a barrier drive; means for detecting motion of the movable barrier; means for detecting when a barrier command signal has been given to the barrier drive; means for storing a commanded state of the barrier drive; means for comparing the commanded state with the motion indicated by said barrier motion detection means, and for indicating if the motion conflicts with the commanded state; and means for generating an alarm signal in response to the conflict indication of said comparing means.
 2. A barrier operator for opening and closing a movable barrier according to claim 1, further comprising means for enabling the alarm signal generating means a preselected time interval following closure of the barrier.
 3. A barrier operator for opening and closing a movable barrier according to claim 2, further comprising means for optically detecting the presence of an obstacle adjacent the barrier and producing an obstacle detection signal in response thereto, said obstacle detection means being inhibited in response to the means for enabling alarm signal generation.
 4. A barrier operator for opening and closing a movable barrier according to claim 1, further comprising a barrier position detection switch for generating a barrier closure signal when the barrier is substantially closed and providing the barrier closure signal to the means for generating the alarm signal indicative of the fact that the barrier has been closed.
 5. A barrier operator for opening and closing a movable barrier according to claim 1, further comprising means for causing the barrier drive to supply a closing force to the movable barrier in response to the alarm signal from the means for generating the alarm signal.
 6. A barrier operator for opening and closing a movable barrier according to claim 5, further comprising means for the barrier drive to cease supplying a closing force after a predetermined time interval.
 7. A barrier operator for controlling a movable barrier, comprising, a down limit detector disposed to indicate whether said barrier is at a closed position or not; memory means for storing one of a set of states of said barrier, the set of states including a CLOSED state indicating said barrier is closed; alarm generation means, responsive to the barrier state stored by said memory means and said down limit detector, for generating an alarm signal when the stored barrier state is CLOSED and said down limit detector indicates said barrier is not at a closed position; and alarm enabling means for enabling said alarm generation means a preselected time interval after said barrier is closed.
 8. A barrier operator according to claim 7, wherein said alarm enabling means is responsive to an indication from said down limit detector that said barrier is closed for initiating the preselected time interval.
 9. A barrier operator according to claim 7, further comprising: down motor signal means, for providing a down motor signal in response to said alarm signal; and a barrier drive responsive to said down motor signal for closing said barrier.
 10. A barrier operator according to claim 9, further comprising: obstacle detector for detecting an obstacle to movement of said barrier, and for generating an obstacle signal in response thereto; and means for disabling said barrier drive in response to the obstacle signal.
 11. A barrier operator according to claim 10, wherein said obstacle detector comprises: an optical light emitter for emitting light; and an optical light detector for receiving the light from said emitter, and generating a signal indicative of whether light is received from said emitter or not.
 12. A barrier operator according to claim 9, wherein said alarm enabling means is disposed to continuously enable without a preselected time delay said alarm generation means after said alarm generation means has generated an alarm signal, and after said barrier drive has closed said barrier in response to said alarm signal.
 13. A barrier operator according to claim 9, further comprising: a barrier drive motion detector for detecting actual motion of said barrier drive and generating a motion signal indicative thereof; wherein said alarm generation means receives the motion signal and generates the alarm signal when the stored barrier state is CLOSED, said down limit detector indicates said barrier is not at a closed position, and said motion detector indicates motion of said barrier drive.
 14. A barrier operator according to claim 9, further comprising: a command signal receiver for receiving a signal commanding said barrier to open, and generating an indication thereof; and means for providing an up motor signal in response to the receiver indication; wherein said barrier drive responds to the up motor signal by opening said barrier; and said memory means stores a state selected from the set of barrier states, other than the CLOSED state, in response to the receiver indication.
 15. A garage door operator for opening and dosing a garage door, comprising: a motor for moving the garage door; a down limit detector, for indicating when the garage door is moved to a closed position by said motor; timer means enabled by the indication from said down limit detector that the garage door is closed, disposed to indicate when a preselected interval has expired; command signal means for receiving a commanded state of the garage door; and a microprocessor responsive to said command signal means for causing said motor to move the garage door to the commanded state, disposed to cause the motor to close the garage door when said timer means indicates the preselected interval has expired, said down limit detector indicates the garage door is not closed, and said command signal means has not received a new commanded state.
 16. A garage door operator according to claim 15, further comprising: a tachometer for detecting rotation of said motor, and for providing an indication thereof to said microprocessor, wherein said microprocessor is disposed to cause said motor to close the garage door when said timer means indicates the preselected interval has expired, said tachometer indicates said motor has rotated beyond a preselected threshold, and said command signal means has not received a new commanded state.
 17. A garage door operator according to claim 15, further comprising: an optical obstacle detector, for optically detecting the presence of an obstacle adjacent the garage door and producing an obstacle detection signal in response thereto, wherein said microprocessor is responsive to the obstacle detection signal to cease causing said motor to close the garage door.
 18. A garage door operator according to claim 15, wherein said command signal means comprises a radio frequency receiver.
 19. A barrier operator for opening and closing a movable barrier, comprising: a barrier drive; a motion detector for detecting motion of the movable barrier; a command signal detector for detecting when a barrier command signal has been given to the barrier drive; circuitry for storing a commanded state of the barrier drive; a controller for comparing the commanded state with the motion indicated by said barrier motion detector, and for indicating if the motion conflicts with the commanded state; and a signal generator for generating an alarm signal in response to the conflict indication of said controller.
 20. A barrier operator for opening and closing a movable barrier according to claim 19, further comprising apparatus for enabling the alarm signal generator a preselected time interval following closure of the barrier.
 21. A barrier operator for opening and closing a movable barrier according to claim 20, further comprising an obstacle detector for optically detecting the presence of an obstacle adjacent the barrier and producing an obstacle detection signal in response thereto, said obstacle detector being inhibited in response to the signal generator for enabling alarm signal generation.
 22. A barrier operator for opening and closing a movable barrier according to claim 19, further comprising a barrier position detection switch for generating a barrier closure signal when the barrier is substantially closed and providing the barrier closure signal to the signal generator indicative of the fact that the barrier has been closed.
 23. A barrier operator for opening and closing a movable barrier according to claim 19, further comprising apparatus for enabling the barrier drive to supply a closing force to the movable barrier in response to the alarm signal from the signal generator for generating the alarm signal.
 24. A barrier operator for opening and closing a movable barrier according to claim 23, wherein the barrier drive ceases supplying a closing force after a predetermined time interval.
 25. A barrier operator for controlling a movable barrier, comprising: a down limit detector disposed to indicate whether said barrier is at a closed position or not; memory for storing one of a set of states of said barrier, the set of states including a CLOSED state indicating said barrier is closed; an alarm generator, responsive to the barrier state stored by said memory and said down limit detector, for generating an alarm signal when the stored barrier state is CLOSED and said down limit detector indicates said barrier is not at a closed position; and an alarm enabler for enabling said alarm signal generator a preselected time interval after said barrier is closed.
 26. A barrier operator according to claim 25, wherein said alarm enabler is responsive to an indication from said down limit detector that said barrier is closed for initiating the preselected time interval.
 27. A barrier operator according to claim 25, further comprising: down motor circuitry, for providing a down motor signal in response to said alarm signal; and barrier drive responsive to said down motor signal for closing said barrier.
 28. A barrier operator according to claim 27, further comprising: obstacle detector for detecting an obstacle to movement of said barrier, and for generating an obstacle signal in response thereto; and for disabling said barrier drive in response to the obstacle signal.
 29. A barrier operator according to claim 28, wherein said obstacle detector comprises: an optical light emitter for emitting light; and an optical light detector for receiving the light from said emitter, and generating a signal indicative of whether light is received from said emitter or not.
 30. A barrier operator according to claim 27, wherein said alarm enabler is disposed to continuously enable without a preselected time delay said alarm generator after said alarm generator has generated an alarm signal, and after said barrier drive has closed said barrier in response to said alarm signal.
 31. A barrier operator according to claim 27, further comprising: a barrier drive motion detector for detecting actual motion of said barrier drive and generating a motion signal indicative thereof; wherein said alarm generator receives the motion signal and generates the alarm signal when the stored barrier state is CLOSED, said down limit detector indicates said barrier is not at a closed position and said motion detector indicates motion of said barrier drive.
 32. A barrier operator according to claim 27, further comprising: a command signal receiver for receiving a signal commanding said barrier to open, and generating an indication thereof; and circuitry for providing an up motor signal in response to the receiver indication: wherein said barrier drive responds to the up motor signal by opening said barrier; and said memory stores a state selected from the set of barrier states, other than the CLOSED state, in response to the receiver indication.
 33. A garage door operator for opening and closing a garage door comprising: a motor for moving the garage door; a down limit detector, for indicating when the garage door is moved to a closed position by said motor; a timer enabled by the indication from said down limit detector that the garage door is closed, disposed to indicate when a preselected interval has expired; a command signal receiver for receiving a commanded state of the garage door; and a microprocessor responsive to said command signal receiver for causing said motor to move the garage door to the commanded state, disposed to cause the motor to close the garage door when said timer indicates the preselected interval has expired, said down limit detector indicates the garage door is not closed, and said command signal receiver has not received a new commanded state.
 34. A garage door operator according to claim 33, further comprising: a tachometer for detecting rotation of said motor, and for providing an indication thereof to said microprocessor; wherein said microprocessor is disposed to cause said motor to close the garage door when said timer indicates the preselected interval has expired, said tachometer indicates said motor has rotated beyond a preselected threshold, and said command signal receiver has not received a new commanded state.
 35. A garage door operator according to claim 33, further comprising: an optical obstacle detector, for optically detecting the presence of an obstacle adjacent the garage door and producing an obstacle detection signal in response thereto, wherein said microprocessor is responsive to the obstacle detection signal to cease causing said motor to close the garage door.
 36. A garage door operator according to claim 33, wherein said command signal receiver comprises a radio frequency receiver.
 37. A barrier operator for opening and closing a barrier comprising: a command signal receiver for receiving barrier open and barrier close signals directing the opening or closing respectively of the barrier; a barrier drive responsive to barrier open and barrier close signals for opening and closing the barrier, respectively; a closed limit detector for sensing the closed state of the barrier; and a barrier controller responsive to received command signals and the closed limit detector for generating an alarm signal when the barrier has been in the closed position and an attempt is made to raise the door when no door open command has been received.
 38. A barrier operator according to claim 37 comprising a timer enabled by the closed limit detector for indicating that a predetermined period of time has passed.
 39. A barrier operator according to claim 37 wherein the barrier drive responds to the alarm signal by applying a closing force to the barrier.
 40. A method of controlling a movable barrier for movement between an open position and a closed position comprising: receiving barrier movement commands including barrier open commands directing opening movement of the barrier and barrier close commands directing a closing movement of the barrier; moving the barrier to the closed position in response to a barrier close command; sensing that the barrier has been moved to the closed position; and generating an alarm signal when the sensing step indicates that the barrier has moved from the closed position, and the receiving step does not indicate that a barrier open command has been received.
 41. The method of claim 40 comprising directing closing movement of the barrier in response to the alarm signal. 